1. Field of the Invention
The present invention relates to a novel ink set for ink jet recording, and to an ink jet recording method which uses the same.
2. Description of Related Art
A recording apparatus for an ink jet method ejects a liquid or a melting solid ink from an outlet such as a nozzle, a slit or a porous film, and records images on an object such as paper, cloth or a film. This recording apparatus has been given considerable attention because advantages such as compactness, moderateness of price and quietness. Various methods have been proposed as methods for ejecting the ink, including a so-called charge control method, a so-called drop on-demand method (a pressure pulse method), and a so-called thermal ink jet method. The charge control method ejects the ink by means of electrostatically attractive force. The drop on-demand method ejects the ink by using the vibration pressure of a piezo element. The thermal ink jet method ejects the ink by using the pressure caused by forming bubbles and developing them at a high temperature. Images of extremely high definition can be obtained by means of these methods.
The ink used in an ink jet recording apparatus is mainly composed of a solvent, a colorant and an additive. The following properties are among those required of an ink; (1) a uniform image which has high resolution and high density should be obtained on the paper without either color bleeding or fogging; (2) clogging caused by the drying of ink in a nozzle tip should be avoided, and ejection response and ejection stability always be satisfactory; (3) the drying characteristics of the ink on paper should be high; and (4) the fastness of images should be high.
Furthermore, high image density, prevention of color spreading in images, and prevention of bleeding between colors are all important factors which need to be taken into account in order to obtain full-color printing which has high definition.
A combination of a first ink containing a dye responsive to a specific pH and a second ink of a pH in which the dye can be precipitated has been proposed for the purpose (for instance, see Japanese Patent Application Laid-Open (JP-A) No. 05-208548). A combination of a first pigment ink containing a dispersing agent responsive to a specific pH, and a second ink of a pH for precipitating the pigment, has been proposed (for instance, see JP-A No. 07-1837). However, it has not been easy to obtain high image density by either of the above methods, and attempts to reduce bleeding between colors have not produced the desired improvements in results.
Among other methods, an ink set obtained by combining a black ink using an anionic dye with a yellow ink containing a cationic dye and a polyvalent precipitant has been proposed (for instance, see JP-A No. 06-57192). However problems have occurred such as nozzle clogging and inadequate ejection stability. A combination has also been proposed of a black ink using a pigment, and color inks, one of which includes a dye or an additive instabilizing the dispersing stability of the pigment of the black ink (for instance, see JP-A No. 2001-152059). However bleeding between colors has not been sufficiently restrained by this method, either.
Thus, a color ink set for ink jet recording has so far yet to be obtained which has high image density; suppresses both color spreading in images and bleeding between colors; can form images of excellent quality; and has an excellent ejection stability.
Therefore, there is a need for an ink set for ink jet recording which can serve high image density in full-color printing which has high definition, suppresses both color spreading in images and bleeding between colors, and also has excellent ejection stability. In addition, there is a need for an ink jet recording method which uses such an ink set and such an ink jet recording apparatus.